Electrocatalytic Reduction of Dioxygen to Hydrogen Peroxide by a Molecular Manganese Complex with a Bipyridine-Containing Schiff Base Ligand

The
synthesis and electrocatalytic reduction of dioxygen by a molecular
manganese­(III) complex with a tetradentate dianionic bipyridine-based
ligand is reported. Electrochemical characterization indicates a Nernstian
dependence on the added proton source for the reduction of Mn­(III)
to Mn­(II). The resultant species is competent for the reduction of
dioxygen to H2O2 with 81 ± 4% Faradaic
efficiency. Mechanistic studies suggest that the catalytically active
species has been generated through the interaction of the added proton
donor and the parent Mn complex, resulting in the protonation of a
coordinated phenolate moiety following the single-electron reduction,
generating a neutral species with a vacant coordination site at the
metal center. As a consequence, the active catalyst has a pendent
proton source in close proximity to the active site for subsequent
intramolecular reactions.